1. Field of the Invention
The present invention relates to a method of and an apparatus for applying a dressing to a cut-off wheel of a cutting machine and, more particularly, to dressing method and apparatus for use in the dressing of an outer or an inner peripheral cutting edge of the cut-off wheel in the form of a disc.
2. Related Art Statement
In the cutting of a semiconductor material such as a silicon ingot, for example, into slices to produce semiconductor wafers, a cut-off wheel having an inner peripheral cutting edge is generally utilized. As shown in FIG. 1 of the accompanying drawings, the cut-off wheel W is in the form of a disc having formed at a center thereof an opening 1, and an inner peripheral cutting edge 2 consisting of an electrically deposited diamond layer of the like is formed along an entire peripheral edge portion of the opening 1. The cut-off wheel W is mounted on a cutting machine (not shown) by means of attaching openings 3 formed along an outer peripheral portion of the cut-off wheel W and is rotated at a high speed by the cutting machine, to cause the inner peripheral cutting edge 2 to successively cut, into the form of a slice, a silicon ingot 4 which is inserted in the opening 1 and is moved in parallel to the cut-off wheel W, as indicated by arrows A.
Such cut-off wheel W decreases in cutting performance due to loading, wear or the like of the inner peripheral cutting edge 2 as the number of cutting operations increases. The decrease in cutting performances causes a variation in thickness and a warp or curvature of the cut products to occur, and this results in the deterioration in quality of the wafers which are final products. Accordingly, it is necessary for such cut-off wheel W to suitably apply a so-called dressing to the inner peripheral cutting edge 2 to remove the loading therefrom and to cause chipping to occur therein, to thereby regenerate or rejuvenate a sharp cutting edge. Conventionally, as the dressing of the inner peripheral cutting edge 2, a dressing method has been adopted in which the inner peripheral cutting edge of the cut-off wheel is caused to cut a highly hard material such as a GC grindstone, a WA grindstone or the like in substitution for the silicon ingot 4 which is a work piece to be cut.
In addition, in general, the warp is caused to occur due to the fact that peripheral side edge portions 2a and 2b (only the side edge portion 2a is shown in FIG. 1) adjacent an end face 2c of the edge 2 are different in cutting resistance from each other and, therefore, the edge 2 is curved and bites in the ingot 4 to cut the same. In order to reduce the warp, a method has also been adopted in which the dressing is selectively applied only to one of the peripheral side edge portions 2a and 2b which is high in cutting resistance, i. e., low in cutting efficiency.
However, it is required for the above-described conventional dressing method to once interrupt the cutting of the silicon ingot 4 by means of the inner peripheral cutting edge 2 at each dressing operation, and this results in a disadvantage of reduction in operating efficiency. Consequently, such problems have arisen that it is difficult to continously obtain products which are uniform in thickness, and the number of inappropriate dressings inevitably increases, to thereby result in the reduction in service life of the inner peripheral cutting edge 2.
Moreover, a large variation or change in warp results in a large variation in the thickness of the products and, accordingly, the above-described selective dressing of the one peripheral side edge portion is required to be performed in such a manner that a slight dressing is successively applied to the one side edge portion at each cutting cycle. It is troublesome to perform such operation manually, and an automatization has been desired. However, an appropriate method of repeatedly supplying a dressing material over a great number of cycles has not yet been proposed, and the automatization has been difficult.